The present invention relates to digital phase comparators, and more particularly, to such comparators intended for use in an integrated circuit broadcast television sync (synchronization) system.
When phase locking one signal to another signal, the initial phase difference between them can be expressed either in the "long path" signless form, e.g. 350 degrees, or the minimum "short path" signed form, e.g. -10 degrees. In general, the unsigned form results in a large variable lock-up time, while the minimum direction or difference signed form will result in shorter lock-up time for the two signals. However, typical prior art phase comparator circuits provide the unsigned form as an output signal. Further, such prior art circuits may not provide information about the exact magnitude of the phase difference and may require that both input signals have a precise duty cycle, or alternatively, that both input signals have identical duty cycles.
It is therefore desirable to provide a phase comparator that provides an output signal having both magnitude and direction information as to the minimum difference of the phase difference of two input signals and which does not require precise duty cycle of both input signals.